A marking gauge is used to mark a line on a surface, where the line is parallel to the edge of the surface. In the case of woodworking, such marks are often made prior to sawing, chiseling or cutting the wood surface. Generally, marking gauges include a fence secured around a shaft. The fence is pressed against the edge of the surface as a sharp marker projecting down from one end of the shaft marks the line. Thus, the fence pressed against the surface edge keeps the marker a constant distance from that edge, allowing a parallel line to be marked. The shaft is typically labeled to show distance (i.e. 16ths of an inch) so that the distance of the line from the surface edge may be adjusted by adjusting the position of the fence along the marking gauge shaft.
Historically, marking gauges have employed a pin or knife-edge as a marker. Generally, pin markers are thought to have advantages when used to make marks along wood grain, and knife-edge cutters, including wheel and blade cutters, are thought to have advantages when used to make marks across wood grain. Wheel cutters are thought to offer advantages when marking shallow marks across the grain because they tend to leave clean mark lines without tearing fibers. Blade cutters are thought capable of cutting deeper in cases where a more pronounced cut or mark is required. Traditionally, blade cutters are fixed directly on the shaft of a marking gauge with a set screw, with the long edge of the blade parallel to the marker's fence. As a result, blade cutters tend to follow the wood grain, in many cases pushing the fence away from the workpiece.
A standard marking gauge is typically limited to a single type of marking method (i.e. pin marking, wheel cutter, or blade cutter). A number of tools perform one or two tasks such as trammels, marking and scribing gauges, but no single marking gauge is capable of performing all three operations with one tool.